The cluster is a set of host working as single host, so the Clusterware is on top and control/manage the hosts, if you have 2 cluster on same host the both software cluster will have concurrency disputing who manages the host and this MUST not occur.

2 CRS software are not allowed on the same nodes. There are several init scripts to start / stop CRS. They cannot point to several GRID HOME at the same time. Also, there is a file storing the OCR disk location. It cannot store 2 version CRS information. Hence, 2 version of CRS should not be allowed on same nodes.